Long Range Neutron-Gamma Point Source Detection and Imaging Using Rotating Detector

A method of detecting radiation comprising the steps of:

• (a) providing a panel monitor comprising a plurality of detector modules stacked vertically, the detector module comprising a close-packed array of small-diameter, thin walled tubes;
• (b) rotating the panel monitor around a vertical axis at between about 0.01 and 5 revolutions per minute;
• (c) recording gamma and/or neutron counts at between about 0.1 and 10 second intervals while the panel rotates;
• (d) processing information regarding the counts and rotation angle using an algorithm to deduce a radiation source size and direction, wherein information regarding neutron counts is processed using the following algorithm:
• (i) recording the monitor rotation angle θi, and neutron count rate yi, at time ti with i taking integer values from 1 to N, where N is the number of measurements over the course of a single rotation,
• (ii) finding parameters a and b that minimize the function −ln(L)=−ln (Πe−fi·fiyi/yi!), where fi is an analytical expression such that fi=a·yti/Σ(yti)+(Σ(yi)−a)·( 1/30), and where yti=yti(θi+b) is the known net angular response of the detector, for each angle θi+b, and
• (iii) once a0 and b0 for which −ln(L)(a0,b0)=min(−ln(L)) are obtained, computing the following quantities:
• the net signal (averaged over all angles) as a0/30;
• the background rate as (Σ(y1)−a0)/30;
• and the source direction angle as b0;
• and information regarding gamma ray counts is processed using the following algorithm
• (i) recording the monitor rotation angle θi, and gamma count rate yi, at time ti, with i taking integer values from 1 to N, where N is the number of measurements over the course of a single rotation,
• (ii) finding parameters a and b that minimize the function χ2=Σ(yi-fi(θia,b))2/yi, where fi is an analytical expression such that fi=a·yti/Σ(yti)+(Σ(yi)−a)·( 1/30), and where yti=yti(θi+b) is the known net angular response of the detector, for each angle θi+b, and
• (iii) once a0 and b0 for which χ2(a0,b0)=min(χ2) are obtained, computing the following quantities:
• the net signal (averaged over all angles) as a0/30;
• the background rate as (Σ(y)−a0)/30;
• and the source direction angle as b0.